Preparation And Modification Of Thermoplastic Polyurethane Pervaporation Membrane For Gasoline Desulfurization

Contrasted with traditional gasoline desulfurization,pervaporation desulfurization is a new kind of gasoline desulfurization technology,which has the advantages of no loss of octane number,low energy consumption,environment-friendly,simple operation and easy industrial scale-up etc.However,many reasons make the pervaporation desulfurization not realize industrialization,including the membrane of low selective for real gasoline that has complex composition,in recent years the membrane module used in the pervaporation has not developed.Membrane material was used as research object,the membrane material including selection,modification,process optimization was researched.Polyvinyl fluoride（PVDF）membrane prepared by laboratory and poly acrylonitrile（PAN）commercial membrane were used as the basement membrane,flat sheet membrane of thermoplastic polyurethane was prepared for sulfur compounds removal from gasoline by pervaporation process.To evaluate the performance,a quinary mixture containing 300 mg·L^-1of thiophene in heptane,cyclohexane,toluene and cyclohexene was tested.The quinary mixture is based on FCC gasoline from Chambroad Holding,which is close to the real gasoline.The preparation process optimization of TPU pervaporation membrane were showed as follows:solid content of 9.1%,the optimum membrane formation temperature of 40°C,the thickness of coating membrane of 300μm,basement membrane of PVDF.The operation process optimization of TPU pervaporation membrane were showed as follows:the optimum desulfurization temperature of 80°C,permeation side pressure of 30-100 Pa,feed flow rate of90 mL·min^-1,then under the optimal condition the flux is 5.49 kg·m^-2·h^-1 and sulfur enrichment factor is 3.53;two kinds of basement membranes were used in the experiment,under the same conditions,the order of membrane flux as follows:PVDF>PAN,the sulfur enrichment factor is in the order of:PAN>PVDF.Membrane surface morphology is smooth,flat and without defects by scanning electron microscopy.Membrane cross-section morphology is consisted of dense active layer and porous support layer.When the solid content is 12.5%,the flux of membrane is 1.76 kg·m^-2·h^-1（a little lower than the flux of membrane with other solid content）,the sulfur enrichment factor of membrane is 6.04.In order to improve the flux of membrane,TiO₂ nanoparticle was introduced to TPU membrane.The flux of TPU/TiO₂ membrane is 4.44kg·m^-2·h^-1（a little higher than the flux of previous membrane）,the sulfur enrichment factor of TPU/TiO₂ membrane is 4.73.The agglomeration of TiO₂ nanoparticle becomes more and more obvious,the number of pores in the membrane becomes more and more,the pore size becomes bigger and bigger by scanning electron microscopy.Chambroad gasoline whose sulfur content is 1700 mg·L^-1was used as separation object.The content of aromatics is higher than other components,is more than 60%（wt%）.Organic sulfide in Chambroad gasoline is mostly consisted with thiophene compounds,more than 99%（wt%）.The flux of TPU membrane was 1.49 kg·m^-2·h^-1 and sulfur enrichment factor was 2.8after testing.Ag₂O was introduced to TPU membrane in order to improve selectivity of TPU membrane for real gasoline,which is based onπ-d complexing.The flux of TPU/Ag₂O membrane was 1.14 kg·m^-2·h^-1 and sulfur enrichment factor was 3.08 after testing.The Electron Microscope Scanning showed that Ag₂O evenly dispersed in the membrane,no obviously agglomeration.Generally speaking,the industrialization prospect of the membrane is great if its flux is greater than 1 and its sulfur enrichment factor is higher than 3.Therefore,TPU/Ag₂O membrane demonstrated great potential for the industrialization of pervaporation gasoline desulfurization.